Is it possible to know the lon/lat coordinates of the origin points of the maps, in order to make a conversion between the ego_pose coordinates and GPS ones?
At the moment all I can offer you is the lat/lon coordinate of the map origin:
Given the fact that the map unit is 1m you could then approximate lat/lon.
Is the map frame of reference aligned with the UTM coordinate axis (i.e. is there any rotation from map to UTM coordinates or just mere translation)? Will be helpful in converting ego to GPS coordinates
The coordinate frame is aligned and the units are meters.
However, there may be some minor local deformations in the map.